Reflector for radiant heat



P 1941- E. .LIBATES ETAL 2,257,366

REFLECTOR FOR RADIANT HEAT Filed Feb. 9, 1940 2 Sheets-Shet 1 Earl J. Bates and John Thciss lnven tors Their Attorney P 1941- E. J. BATES ET AL l REFLECTOR FOR RADIANT HEAT Filed Feb. 9, 1940 2 Sheets-Sheet 2 0 Q My Earl J. Bates and john S. Thciss Inventors Their Attorney Patented Sept. 30, 1941 REFLECTOR FOR RADIANT HEAT Earl J. Bates, Oakwood, and John S. Theiss, Dayton, Ohio, assignors to The National Cash Register Company, Dayton,-

of Maryland Ohio, a corporation Application February 9, 1940, Serial No. 318,200

- Claims.

This invention relates to reflectors and more particularly relates to heat reflectors for directing heat radiation from a heat source.

Radiant heat from incandescent sources is now commonly used in ovens for baking finishes, such as enamels and lacquers, and for other manufacturing processes requiring the application ofheat. Such ovens are usually tunnel-like in character so that a conveyor may a carry objects through the tunnel, the baking taking place as the object is moving. Incandescent electric lamps as the heat sources are arranged around the tunnel in regular banks, each lamp being supplied with a reflector to direct the heat rays to the central axis zone of the tunnel along which the objects pass. The cross section of such a baking oven tunnel ordinarily is of a shape best suited to conform to the shape of the objects to be carried therethrough, for more even baking.

As most of the useful heat in such ovens is direct or reflected radiant heat, rather than convected heat, it is important that the direct radiation and the reflected radiation do not escape from the open ends of the tunnel. In maintaining a high oven temperature, the heat sources must be placed as close together as possible. With the ordinary parabolic oven reflectors now in use, there is an energy loss due to direct and reflected radiation out the ends of the tunnel, as proved by a person standing at the end'of the tunnel being able to see the visible portions of the heat rays. If a common parabolic reflector is deepened sufllciently to prevent this energy loss from the ends of the tunnel, the mouth of the reflector will be too wide for use in an oven requiring the heat sources to be close together. Another requirement in such an oven is to provide a reflector of such shape that it may be used in cooperation with others of the same type to produce an even and diffuse heating zone that reaches all sides of a transported object.

Therefore, the principal object of the invention is to provide an efllclent directional reflector for heat rays for use as one of a bank of similar cooperating reflectors in a baking oven.

Another object of the invention is to provide 'a reflector of high efficiency in directing radiant heat in a radiant heat oven, which reflector has a mouth that is narrow relative to its depth.

Another object of the invention is to provide a reflector especially adapted to be used to refie-ct heat rays emanating from an incandescent annular filament, the annulus and the reflector having the same axis.

Another object of the invention is to provide a deep but narrow-mouthed heat reflector for a source of radiant heat whereby substantially all of the radiant heat produced is diffusely directed in a narrow beam without side loss.

With these and incidental objects in view, the invention includes certain novel features of construction and combinations of parts, the essential elements of which are set forth in appended claims and a preferred form or embodiment of which is hereinafter described with reference to the drawings which accompany and form a part of this specification.

Of said drawings:

Fig. 1 is an axial section ofthe reflector and a typical radiant heat source.

Fig. 2 shows the superimposed curves from which the contours of the reflector are generated.

Fig. 3 is a representation of a group of reflectors in cooperative lateral arrangement.

Fig. 4 is a cross section through a typical tunnel baking oven showing the arrangement of the reflectors in relation to objects passing through the oven.

General description The reflector 20 (Figs. 1 and 2) is a shell formed from the generation, on axis 2|, of a compound curve consisting of a portion of a parabola 22 merged with a portion of a second parabola 23, in turn merged with a portion of a circle 24 which itself is tangent to a straight line 25 positioned at an angle of '7 degrees from axis 2|, on which axis the focus 26 of parabola 22, the focus 2'! of parabola 23, and the center 28 of circle 24 lie. 1

The foci 26 and 21 and the center 28 are positioned relative to the origin 29 of the parabola 22. If this origin 29 be taken as the zero crossing of the X and Y coordinates, axis 2| being the X coordinate, then parabola 22 will be expressed in the following terms:

where A equals the distance from focus 21 to the origin 30 of parabola 23; parabola 23 will be expressed as Y 4AX-.96A =0 and circle 24 will be expressed as X 8AX+Y +3.04A =0 Parabola 22 is tangent to the vertical or Y axis. The straight line 3| indicates the portion of the reflector which is cut away to admit the shank of electric lamp 33.

Those portions of the parabolas 22 and 23, circle 24, and straight line 25 merged in a smooth line to form the compound curve from which the reflector is generated, are shown by that portion of the heavy solid line of Fig. 2 between points 34 and 35. Although the exact shape of the reflector is given, it should be understood that approximations to said exact shape which give the same result are to be considered within the scope of this invention.

Electric lamps for heat sources are generally provided with an annular filament, to be rendered incandescent, which filament is oriented so that the filament and the reflector are coaxial. Such a filament 36 is shown diagrammatically in Figs. 1 and 2 as positioned very slightly in front of focus 26, which will give a pattern and field of heat rays as shown by the reflectors 31, 38, and 39 (Fig. 3). Although the annular type of filament is best for this reflector, any suitable type may be used.

In Fig. 4, a cross section of a cylindrical tunnel oven is shown with applicants reflectors installed, to. illustrate how the lamps and filaments are hidden, eliminating direct radiation from the ends of the tunnel. Fig. 3 shows how the narrow mouth of the reflector with relation to the depth permits a closer arrangement of the lamps and consequent greater density of heat rays in the baking zone. The reflected rays as well as the direct rays are kept within a cone which is relaatively narrow with relation to the oven diameter, keeping the heat rays from becoming lost out the ends of the oven.

By use of applicants reflector, oven temperatures have been increasednearly 100% over oven temperatures obtainable with simple shallow parabolic reflectors using the same amount of electric energy and the same type of electric lamp.

By coating the reflecting surface with burnished gold 4| (Fig. 1) the reflecting power of the surface is increased for those wave lengths of the radiation spectrum most useful in the baking of finishes.

In conveying an object 42 through a tunnel type of oven as shown in Fig. 4, with the lamps positioned as shown in Figs. 1 and 2, the sides of the object facing the lamps receive more direct rays than do the leading and trailing ends of the objects. To overcome the uneven heating,-

certain reflectors, preferably in the center of the oven, have the lamp set forward as illustrated by the lamp shown in reflector 40 (Fig. 3) which projects a larger cone of direct and reflected rays, which strike the ends of the passing objects more directly than the sides, the two methods of focusing combining to produce an even baking over the entire surface of the transported object.

For a concrete interpretation of the general equations given above for determining the shape of the reflector-generating curve for a reflector of any wanted size, the dimensions of a reflector suitable for a standard 250-watt electric lamp will be given. If the mouth 42 (Fig. 2) be ten inches across, the depth of the reflector from point 43 to point 44 will be approximately 8 inches. The distance from vertex to focus 21 will be 1.25 inches; the distance from originvertex 28 to focus 26 will be 2 inches; and the distance from origin 29 to center 28 will be 5 inches.

' surface is tangent to said While the form of mechanism herein shown and described is admirably adapted to fulflll the objects primarily stated, it is to be understood that it is not intended to confine the invention to the one form or embodiment herein disclosed, for it is susceptible of embodiment in various forms, all coming within the scope of the claims which follow.

What is claimed is:

1. A reflector having a surface the axial section of which is a compound curve derived from the merger of portions of four conic sections having the same axis, said portions of conic sections starting at the vertex of the reflector and proceeding toward the mouth being first, a parabola whose origin is at the vertex of the reflector, a second parabola whose origin is behind the vertex of the reflector, a circle whose center is to the front of the focus of the first mentioned parabola, and an axial section of a right circular cone having its vertex behind the vertex of the second mentionad parabola.

2. A reflector having a burnished gold reflecting surface the axial section of which is a compound curve derived from the merger of portions of four conic sections having the same axis, said portions of conic sections starting at the vertex of the reflector and proceeding toward the mouth being first, a parabola whose origin is at the ver- ,tex of the reflector, a second parabola whose Y=4AX.96A=0 a circle whose equation is X -8AX+Y +3.04A'=0 and lines tangent to said circle and sloped outwardly and forwardly from the rear of the reflector at an angle of 7 degrees from the axis, the vertex of the first parabola being tangent to the Y axis.

4. A reflector having a burnished gold reflecting surface, the contours of which surface are like the surface of a body formed by the merger of a section of a first paraboloid with a section of a second paraboloid having a shorter focus, which second paraboloid has its vertex to the rear of the vertex of the first paraboloid, a section of a sphere whose center is in front of the focus of the first mentioned paraboloid and whose second paraboloid, and a section of a right circular cone of 14 degrees, tangent to said circle, all of said sections being co-axial.

5. A heat reflector consisting of a shell whose inner reflecting surface is symmetrical with a central axis, the contours of said shell being described by the generation of a compound curve on said axis, said compound curve resulting from the smooth merging of portions of two parabolas havingthe equations of where the Y axis is tangent to the vertex of the parabola defined by the first equation, the said second parabola merging with a portion of a circle having an equation the said circle having tangent thereto an axial section of a right circular cone the vertex of said cone having an angle of 14 degrees pointed toward the rear of the reflector.

6. A directional heat reflector for use with a co-axial annular incandescent filament, a cross section through said reflector consisting of a first portion forming a parabolic vertex, a second parabolic portion merged to the first parabolic portion to the rear of the parameters of the parabolas of the first and second parabolic portions, a circle portion tangent to the second parabolic portion and whose center is forward from the said parameters, and an axial portion of a right circular cone of 14 degrees whose vertex lies to the rear of the reflector and having its sides tangent to the circle, and having the axis of the cone, the axes of the parabolas, and the center of the circle portion lying on a straight line, the parameter of the first parabolic portion and the center of the circle portion being located a substantially reduce reflected radiation out the width and having its best focal point deep in the reflector so there will be little or no energy loss from the tunnel ends by direct radiation from such focal point and very little loss from the tunnel by reflected radiation.

9. A parabolic reflector having a reflecting shield on its mouth the contours of which shield are. generated by a section of a circle tangent to the parabolic mouth and an axial section of a right circular cone having its mouth end at an angle to redirect side reflection toward the axis of the projection whereby a narrow cone of rays may be obtained from a deep reflector without loss due to repeated reflection, the center of the circle and the axis 'of the cone being on the axis of the reflector.

10. A parabolic reflector having smoothly merged with its mouth end a reflecting and flared deepening collar for hiding a heat source located at the principal focal point of the reflector so as to reflect the side direct radiation to substantially within the cone of the rays reflected from the parabolic reflector, said collar being formed like the surface of a section of a right cone having an apex angle of approximately one-fourth of a radian.

EARL J. BATES.

JOHN S. THEISS. 

